A picture is worth the money of a piece of equipment, do you believe it?
Two days ago, I met a customer and bought a big tie rod expansion joint, which leaked within two months after installing it. After removing it, the bellows was directly punched through by the medium. People from the manufacturer checked in the past and found that the direction of the deflector was installed backwards. The customer is still wronged: I saw the drawings, isn't the arrow facing that way? As a result, the arrow refers to the flow direction of the medium, and he pretends to be in the opposite direction. You say it was wrong or not? A clearly marked thing on the installation diagram, but no one looked at it closely. Finally, I bought a new one. The construction period was delayed for half a month and it cost tens of thousands more. So I said, if you really understand the metal expansion joint installation diagram, you will save not only equipment money, but also your life of working overtime.
Symbols and annotations, which ones do you look at?
Don't let the lines and arrows full of the diagram intimidate you. There are only a few core messages. First, the direction of the arrow-that represents the direction of the medium flow. The opening of the guide tube must be facing the medium, otherwise the bellows wait to be flushed and perforated. Second, locate the position of the bolt or tie rod nut. The pre-stretched or pre-compressed dimensions, such as "stretch X mm", are usually labeled on the drawing. This size is a lifeline for the compensator to work properly. If you tighten it casually, or don't adjust it at all, the expansion joint will be dead. Third, the position of the support-the fixed support and the sliding support are clearly drawn in the drawing. If one is installed wrong, the stress of the whole pipe system will be messed up, and it will be a matter of time before the pipe will shift and the flange will tear.
For example, the universal corrugated expansion joint and the double hinge transverse expansion joint have completely different marks for the support on the installation diagram. The former requires one end to be fixed and the other to slide, and the latter may also have to add guide brackets. These details, one symbol and one annotation on the diagram, are to tell you: You can't be careless here.
Different working conditions, the attention on the installation drawing is very different
High temperature, high pressure, large diameter, direct burial, the installation drawing of each working condition has its own "hidden rules". Take high-temperature axial expansion joints, for example, pre-tension should be considered during installation. The reason is simple: when the pipe heats up and expands, the expansion joint has to be "elongated" a little first to leave room for thermal expansion. If you don't do pre-stretching, it will be heated up and directly dead, and the bellows will deform or even crack. The pre-stretch amount will be marked on the diagram, just follow the adjustment.
Let's talk about the directly buried (fully buried) expansion joint. This thing is buried in the ground, and the picture will specifically indicate the outer protective layer and anti-corrosion treatment. Backfill soil cannot be smashed with large stones, but must be tamped in layers to prevent smashing the bellows. Some customers think it doesn't matter, but as a result, they corrode and perforate within a few years of being buried.
The metal corrugated expansion joint in cement industry is more special, with large dust and high temperature. The fitting gap of wear-resistant guide tube is additionally marked on the installation drawing. When the gap is small, it gets stuck, and when it is large, it leaks ash. The manufacturer has drawn all the tolerances. If you can't read it or don't read it, then wait for rework.
Three common pits, how many have you stepped on?
- Myth 1: The screw does not need to be disassembled, and it is more stable when fixed.Those set screws at the factory are for transport protection and must be loosened or removed after installation. Otherwise, the compensator can't move, and the thermal displacement of the pipeline is all carried by the bellows, which is strange if it is not bad. What about that? Compare the installation drawing, find the label of "Remove the positioning piece", and screw it off.
- Myth 2: Tighten the tie rod nut casually, the tighter the better.The tie rod of the expansion joint of the large tie rod absorbs the lateral displacement, and the nut can be adjusted to the size required by the drawing. Screwed to death, the tie rod loses its function, the lateral displacement is fully pressed on the bellows, and the life is directly cut in half. It will say "Adjust to X mm" on the picture. Take a ruler to measure it, don't rely on the feel.
- Myth 3: Run directly after installation, without suppressing leak test.Pressure testing is necessary, but it should be noted that the expansion joint is not distorted by external force before pressure testing. Especially for the transverse expansion joint of compound hinge, the misalignment of hinge direction will lead to additional stress, and the bellows may burst directly during pressure test. Installation diagram has hinge direction indication, wrong installation? Take it down and start over.
After installing, I have to go back and check
Don't think it's done when you're done. The metal expansion joint installation diagram is not only for you to see when installing, but also for checklist after installation. Step 1: Check all the bolts – Are the positioning bolts removed? Is the tightness of the tie rod nut adjusted as shown? Step 2: Manually push the pipe and see if the expansion energy saving freely expands and deflects? If it's stuck, you have to check it. Step 3: Water pressure or air pressure test, stare at the bellows surface during pressure holding, is there any leakage? If you have it, shut down.
Listen to the sound more during the trial run. If you hear an abnormal impact sound, it may be that the guide tube is misaligned, or the tie rod is interfering with the bellows. In fact, the installation drawing implies solutions to these problems-such as the matching clearance marking of the guide tube and the swing angle range of the tie rod. The point is that you have to understand it first.
Alas, to put it bluntly, drawings are the "instructions for use" of manufacturers, but they are also the "heavenly book" of many people. Next time you get the metal expansion joint installation diagram, don't rush to get started. Spend ten minutes running through the symbols, arrows, and dimensions, and you will save more than just maintenance costs.